It appears to us that you added tubes of colored frosting and some amount of paste food coloring to both batches of your Betty Crocker frosting. It is not clear if the tubes of colored frosting were also from Wilton, the wonderful baking company based outside of Chicago, but the food coloring clearly was.
So we asked the folks at Wilton, who said that the only differences between the colored versions of their products is the FD&C colors used to tint them (FD&C stands for the Food and Drug Administration’s Food, Drug, and Cosmetic Act, if you were curious…). In any event, the Wilton folks do not think the color difference would cause one icing to melt while the other performed as expected.
They were willing to guess that you may have stirred the orange batch much more aggressively than the purple batch, which might have caused it to be thinner and more runny.
Our bet (and it pains us to question your word) is that you cooled the batch of cupcakes destined for purple more thoroughly, and that the orange cupcakes had a bit of residual warmth that melted the icing. We cannot stress enough the need for cakes and cupcakes to be completely cool before they are frosted; otherwise you are inviting cake-decorating disasters and puddles of goo.
The only other option is that you used two different kinds of colored frosting (maybe one from Wilton and one from another manufacturer), which differed in more than just food coloring, and this accounted for your disappointment. If you used a regular frosting for the purple and a gel frosting for the orange, that could well account for the difference.
And since when are the official Halloween colors orange and purple? We definitely did not get that memo.